Beattie & Howland's recent studies of the bionomics of some tree-hole mosquitos emphasize the importance of the food factor, total organic nitrogen, and the apparent lack of correlation between hydrogen ion concentration and larval incidence. In Queensland mosquitos selecting such breeding-places are with a few exceptions distinctly arboreal, and the presence of domestic mosquitos in tree-cavities is dependent upon proximity to human habitations. It is a curious fact that when this is the case both Aëdes argenteus and Culex fatigans will breed in smaller accumulations of water than Aëdes notoscriptus does.

Appended herewith are the results of a recent survey made in midsummer of trees situated within the Brisbane Area of 385 square miles. Pine trees and gum trees do not lend themselves to the production of cavities and therefore offer very little opportunity for breeding.

The poincianas hold the highest actual percentage, but on account of the far greater number of figs containing potential breeding cavities, the latter constitute a greater actual menace. The amount of water contained in each cavity varies considerably with the time of year.